I have a 1995 z/28 4l60e has 20,000 miles on the rebuild. It is hitting the rev limiter before it shifts and it slips going into 2,3,od but it only dose it sometimes . I have 4.10 posi rear and I have noticed it doesn't take off near as hard as it used to . Six months ago I put a big cam in and it ran stronger than ever but not now. Could this be a torq converter problem or a pump. I don't know a lot about transmisson when they rebuilt it they used cavlar clutches and bands corvette servo and shift kit and it shifted hard like total sideways hard.. I just changed fluid and filter and didn't find any trash in the pan or filter and it didn't help the problem. Oh and it only shifts like that at wide open if your not wide open it shifts hard and no slip. Any help would be greatly appreciated thank you

 

Did it just start doing this or has it been since the rebuild, you say it has 20,000 miles on it now so what did it do right after the rebuild.

 

Now this was a decade ago but when I had my tranny done a shop pushing Kevlar was proof they were BAD. Possible someone came up with a new way to use kevlar but seeing as they sold you a STOCK servo as an "upgrade". All LT1 cars came with the Vette servo, even grandma's Roadmaster wagon.

HARD shift in a 4L60E are again a mark of incompetence, shifts should be quick and positive but not "hard".


The vast majority of shops, even "performance" shops are really shitty at rebuilding the 4L60E, sounds to me like you are about to find this out the hard way. The symptoms you describe are not converter, they are crappy tranny build.

MANY of us made this mistake before you, try and trust someone local, get totally screwed then get a real professional like Rossler, Dana at ProBuilt, Chuck formerly of FLT etc. to built one right. I got 16 months behind near stock power out of my first rebuild, that was a decade ago and the ProBuilt I bought next has stood up to a lot more power for a lot longer.

 

Right after it was built it ran strong when I put the 4.10 gears in it turned into quite a handful to drive but super fun when changed from 1 to 2 no hesitation no stutter shift but after a wile it started t slip in 3rd after rev limiter. I can be riding along at about 50 mph stomp the throttle kicks down no slip and if I'm riding down the road hold it in second or 3rd and floor it and no slip so the only time it slips is when it shifts .hope that helps

 

I'd first try and re-tune the trans for those gears. The PCM determines shifts, by load, TPS, RPM and MPH. At least on My Suburban it does, disconnect the speed mag pick up and it wont automatically shift at all. When you set your shift speed to 45mph in first at WOT, the it'll stay in first to 45 MPH at WOT, rev limiter be damned. Going from 3.23 to 4.10 will screw that tune. 3.73 - 4.10 is less noticeable, but will still mess up on WOT shifts.

 

I will give that a try .. I wish I would have gone with 3.73s gears much more road friendly just regular street driving I'm in over drive before most cars are still in second gear but it is a lot of fun . Thank you for the help I will let you know what I find .

 

Contrary to popular belief gears do not meaningfully impact the shifting if the pcm is left unmolested, this is because the VSS feedback is at the output shaft, not at the tire. The car has no idea the rpm/mph relationship is out of sync.
Changing gears will have an effect on load for output rpm(what VSS sees) which would have some slight effect but not banging off the rev limiter or anything.
If the VSS was at the tire then changing gears would have you banging the rev limiter before shifts and all.

 

Doh! I'm an idiot. Disregard my previous post. Good Catch!

Still though, why the sudden change with the 4.10's? Load? If a larger throttle body causes transmission shifting issue due to kPa, then wouldn't the reduced load on the trans do similar things?

 

Years ago I spoke to supposedly one of the engineers that was involved in the development of the software for our cars, Of course way back then in around 95 people were still having problems when switching to steeper gears or higher stall, According to him, it had nothing to do with load or mph but that the algorithms in the software was unable to keep up with the now faster spool up of the rpms, such as calculated at the shaft, another words, it lagged behind trying to calculate thus causing the shifting problems, dont know but kinda made sense. This is why usually you have to lower your shift points to get the proper rpm that you want it to shift at, basically by the time the pcm calculates the rpm or whatever it does, its like, oh **** its time to shift thus the delay..

 

The LT1 OBD1 pcm certainly is slow. That is my understanding of the "stall wall" issue so many of us have faced.

 

Thanks guys. Should I take some where to program the shift points or is this something I can do and if so how? I hope these ? Don't make me sound stupid!!! But I know some of you know a lot about this car I don't . Thanks again for all your input

 

First off the shop will need to have tuning software and a "competent tuner" which are hard to find these days, If it is the stall wall issue as 96 said, then its a trial and error approach.

 

I meant I think stall wall is a result of a slow pcm.

I think the problems he is having are from a bad transmission built.

 

Yes I agree, stall wall is the result of the slow pcm but I also think its a bad rebuild.

 

But there is no "stall wall" on obd2 pcms... if they are in fact the same or close to the same pcms then slow doesn't correlate.

 

I guess it could be a transmission gone bad but I haven't driven in about 2 weeks and I took today out and it shifts perfect hit 2 smoked the tires hit 3 and and all is good came home same thing drove good . It doesn't do it every time is there anything that would cause this besides bad transmission..?

 

Maybe it is heat related and you got some worn valve bores that don't seal as well when the fluid is hot or something like that.

 

I am going to pull it and have them look at it. I have another question . I have a pro comp cam I can't find my cam card but I am pretty sure it was a 511 and I think it was 276 not sure the power range kicks in at 2,400 rpm what stall should I use ? I wish I had more info on cam but I know it beats the ground . I had it done in fl and I live in N.C now they didn't have a copy of the order or cam card

 

Were the trans pressures increased when the converter was installed? I had similiar issues and raised the Max press from 90 to 100 and it made a noticible difference. However my trans is old and wearing out, not recently rebuilt.

 

Yes there is, granted in rare occasions, but even in the LS, I had a few with large stalls (4500) and they were spraying, I had to lower the shift points in order to have the tranny shift at the required rpms.